Sexual reproduction in the water mold Achlya is controlled by specific steroidal hormones antheridiol and the oogoniols. These compounds have been shown to be biosynthesized from fucosterol which is the major steroid present in Achlya. We now propose to investigate intermediates on the biosynthetic pathway from fucosterol to oogoniol. Plausible intermediates such as 29-hydroxy fucosterol, 29-oxo-fucosterol, 29-hydroxy sitosterol, 29-hydroxy clionasterol and analogs with additional hydroxyl groups on the tetracyclic nucleus will be synthesized. They will be labelled with tritium and fed to Achlya to determine if they can be converted to oogoniol. Antheridiol is known to be metabolised to two products by Achlya. Attempts will be made to identify these metabolites.